In recent years, optomagnetic recording media have become widely utilized as large-capacity data files etc. in the form of an optomagnetic disk in which recording and reading can be done by means of a laser light beam.
An optomagnetic recording medium is usually made by forming a recording layer and a protective layer on a transparent substrate plate by means of a film-forming technique such as sputtering. Optomagnetic recording media thus produced are used as they are, i.e., as single recording media, in some cases. In other cases, two single recording media are bonded to each other on the sides thereof remote from the substrate plates through an adhesive layer to give a double-side information-recording medium, which is then used.
In order to effectively utilize an incident light beam during recording and playback operations thereby heightening the C/N ratio and also obtaining recorded bits of well symmetrical shapes, when the light beam is being allowed to enter from the substrate plate side, there has been proposed an optomagnetic recording medium having a reflection layer as the uppermost layer, i.e., the layer farthest from the substrate plate. Such a reflection layer is being employed not only in single optomagnetic recording media but also in double-side information-recording optomagnetic recording media. Such recording media are disclosed, for example, in JP-A-57-120253. (The term "JP-A" as used herein means an "unexamined published Japanese patent application".)
Such a reflection layer generally is a thin layer of a highly reflective metal such as, for example, Al, Au, Cu, Pt, Ta or Ti, or an alloy thereof. Of these, primarily, Al and Cu are being studied because they are cheap and comparatively good in reflectance and heat conduction.
However, Al and Cu have a problem in that they are relatively likely to corrosion, so that their reflectances will be gradually lowered during use or storage.
In attempts to solve the above problem so as to improve the corrosion resistance of reflection layers, there has been proposed a method in which a reflection layer is made from an alloy, and a method in which a reflection layer is surface-treated. However, the corrosion problem has not yet been solved sufficiently. With respect to the method employing an alloy reflection layer, JP-A-62-239349 and JP-A-62-295232, for example, disclose methods in which alloys of Al and a metal such as Mg, Si, Fin, etc. are employed, but these methods are not sufficiently effective. That is, optomagnetic recording media manufactured by these methods are defective in that when they are stored in an environment having a high temperature and a high humidity for an accelerated deterioration test, corrosion spots are developed in the surfaces of the reflection layers in a relatively short period of time and this results in a sporadic decrease in reflectance, thereby causing dropouts (bit error rate (BER)) to increase.